Low-profile additives for thermosetting polyester compositions

ABSTRACT

A curable polyester molding composition incorporating an elastomeric low profile additive dispersed in voided rubbery particle form throughout the composition is used in association with a compatibilizing agent to form a molded thermoset article having very smooth, light reflective, class A surfaces and having a matrix fracture energy which is comparable to articles formed from similar or identical molding compositions which are free of low profile additives. The low profile additive is an epoxidized elastomer or block copolymer having at least one flexible elastomer block and one monovinyl aromatic block. The compatibilizing agent is a copolymer having a diene polymer backbone which is compatible with the elastomer or the flexible diene block of the low profile additive, with constituents which are compatible or reactive with the polyester being grafted or adducted onto the diene polymer backbone. The compatibilizing agent improves the solubility of the low profile additive in the uncured molding composition to promote good dispersion, to promote and maintain small particle size of the low profile additive, and to enhance compatibility between the cured polyester matrix and the low profile additive, thereby providing a low profile mechanism wherein shrinkage compensation during curing of the composition occurs almost exclusively through voiding of the small tough elastomeric particles of the low profile additive dispersed in the cured polyester matrix.

FIELD OF THE INVENTION

The invention relates to curable molding compositions and to a processfor utilizing the same to form molded thermoset articles which undergolow or practically no shrinkage during curing, which are characterizedby a very smooth surface, and which have excellent mechanical propertiesgenerally because of their morphology. More particularly, the inventionconcerns the use of certain modified elastomers as low profile additivesto compensate for shrinkage during the curing of unsaturated polyesterthermoset compositions, thereby keeping the surface of the moldingcomposition in contact with the mold surface to provide a cured articlewhich has a smooth surface without significantly reducing the fracturetoughness or other mechanical properties as compared with moldedthermoset articles formed from unsaturated polyester compositions whichare free of any low profile additives.

BACKGROUND

Because of its relatively low cost and inherently high strength toweight ratio, polyester molding compounds, including sheet moldingcompounds and thick molding compounds, are being utilized withincreasing regularity in the automotive and appliance industry as areplacement for steel. These molding compounds generally compriseunsaturated polyester resin, a crosslinking agent such as styrene,reinforcing fibers such as glass fibers, fillers, a catalyst to enhancecuring and various other additives. For applications wherein a smoothClass A surface finish is required, such as for automotive body panels,low profile additives which offset the shrinkage effects ofthermosetting polyester molecules during crosslinking are used. Theselow profile additives counteract the effects of shrinkage to prevent themolding composition from pulling away from the mold surface which wouldcause waviness, voids or other surface irregularities.

Conventional low profile additives used for reducing shrinkage and forproviding improved surface finish for thermosetting resin systemsgenerally fall within one of two major categories. A first generalcategory includes additives which are compatible with the precrosslinkedthermosetting system. Examples of low-profile additives which arecompatible with styrene crosslinkable unsaturated polyester systemsprior to cure include polyvinyl acetate, polycaprolactone, andpolyurethane. Compatible low-profile additives, particularly polyvinylacetate, have been found to achieve excellent low-profile effect,exhibiting low or zero shrinkage and providing good surface appearance.However, such systems usually exhibit significant reductions inmechanical properties such as fracture toughness, tensile strength,modulus and strain to failure and the same is attributable to themorphology which arises from the mechanism by which low-profile effectis achieved. During the early stages of curing for a thermosetting resinsystem, employing a compatible low-profile additive, as crosslinkingproceeds, a high molecular weight polymer network is formed which phaseseparates from the initial solution and forms spherical microgels ornodules with the initially compatible low-profile additive and unreactedcrosslinker and resin forming a continuous phase. As the cure progressesto a more advanced stage, the nodules grow and form a macro-networkstructure wherein individual nodules are connected to neighboringnodules by comparatively small resin bridges, with the surroundingcontinuous phase, largely depleted of resin and crosslinker, nowcomprising mostly the low-profile additive. During the latter stages ofthe cure, the crosslinked polymer having a macro-network structurebegins to shrink creating stresses which are transferred to thecontinuous, low-profile additive phase, causing the formation ofmicro-voids or cavitations in the low-profile additive continuous phase.The final cured composition can be described as having a popcorn-likestructure or morphology wherein the crosslinked domains comprisenodules, each of which is coated with a thin film of the cavitatedlow-profile additive and is connected to neighboring nodules byrelatively small bridges of crosslinked resin. The greatly reducedcontinuity of the phases and the ease with which the bridges can bebroken explains the severe reduction in mechanical properties.

Thus, while conventional compatible low-profile additives such aspolyvinyl acetate are very popular because of their excellent shrinkagecompensation effects and because of the high quality surfaces producedtherewith, their use is limited by the resulting morphology which leadsto reduced toughness and strength.

The second major category of low-profile additives are those additiveswhich are noncompatible with the initial precrosslinked thermosettingresin systems. Examples of noncompatible low-profile additives includepolyethylene, polystyrene, polymethylmethacrylate, polyvinyl chloride,butadiene and block copolymers of styrene and butadiene. Thenoncompatible low-profile additives function differently from thecompatible additives and provide an entirely different morphology andmechanism for achieving shrinkage compensation and low profile effect.Noncompatible low-profile additives when used with pre-crosslinkedthermosetting resin systems become dispersed as discrete particleswithin a continuous phase comprising the crosslinker and crosslinkableresin, and ultimately provide a structure wherein the low-profileadditive is dispersed as a discrete discontinuous second phase within acontinuous crosslinked polymeric matrix. Noncompatible low-profileadditives generally have been found to provide better mechanicalproperties than the compatible low-profile additives, but do not achievecomparable low-profile effect. Other disadvantages with conventionalnoncompatible low-profile additives is that because they arenoncompatible, i.e. insoluble, with the precured thermosetting solution,the low-profile additive particles can tend to segregate and agglomerateleading to nonuniform properties and surface appearance and paintadhesion problems. Moreover, such additives generally have highmolecular weights and consequently form large particles, which, likeagglomeration, create surface appearance and paint adhesion problems.Also, the large particles of conventional noncompatible low-profileadditives may not be well bonded to the surrounding crosslinked polymermatrix leading to cavitation at the interface between the particles andthe matrix, which is less effective for arresting crack propagation thancavitation within the particle.

Thus, while conventional noncompatible low-profile additives achieve abetter morphology than conventional compatible low-profile additives,which leads to better mechanical properties, they do not provide verylow or zero shrinkage as do the compatible additives. Also, typicallythey have surface appearance and paint adhesion problems which oftenpreclude their use despite some improvement in mechanical properties.

Accordingly, given the present state of the art, it would be highlydesirable to create an additive for thermosetting polymeric compositionwhich counteracts shrinkage during the cure and provides a class Asurface finish, while at the same time retaining the good mechanicalproperties of the polyester.

SUMMARY OF THE INVENTION

It has been discovered that certain elastomers, when appropriatelymodified and used with a suitable compatibilizing agent, are capable ofacting as effective low profile additives for unsaturated polyesterthermosetting compositions. The low profile additives of the inventionwhen used in combination with a suitable compatibilizing agent formsmall discrete domains within a continuous crosslinked polyester matrixduring curing of the thermosetting composition, with cavitation andshrinkage compensation occurring substantially within the discreteelastomeric domains thereby preventing the mold composition from drawingaway from the interior surfaces of the mold, and consequently providinga very smooth, highly reflective class A surface finish. Moreimportantly, excellent surface characteristics are obtained withoutsignificantly sacrificing mechanical properties because shrinkagecompensation occurs entirely within a relatively tough elastomeric phasewhich is dispersed throughout the matrix as a discrete discontinuousphase, i.e. small particles. Because of the resulting morphology, themolded article has better mechanical properties than an article formedwith conventional low profile additives, while achieving excellentsurface characteristics.

DETAILED DESCRIPTION

The elastomers used to form the low profile additives of the inventioncan be homo- or copolymer elastomers, or thermoplastic di-, tri- ormultiblock copolymers, that is, A--B type diblock copolymers, A--B--Atriblock copolymers, or A-- --B--A)_(n) multiblock copolymers wherein nis from 2 to about 8, or mixtures thereof, having at least one flexible"B" block which is generally a homopolymer of a conjugated diene, or acopolymer of two or more conjugated dienes, or a copolymer of at leastone conjugated diene and various other addition polymerizable monomers.Preferably, the elastomers or block copolymers used to form the lowprofile additives of the invention are generally thermoplasticelastomers having a flexible block or segment containing olefinicunsaturation.

Examples of suitable elastomer homo- or copolymers include those madefrom one or more conjugated diene monomers having from 4 to 12 carbonatoms with polybutadiene and polyisoprene being preferred and have amolecular weight of from 15,000 to 200,000 and preferably from about50,000 to about 150,000.

Suitable conjugated diene monomers for making the flexible block of theblock copolymer contain from about 4 to about 12 carbon atoms, and morepreferably from about 4 to about 8 carbon atoms. Specific examples ofsuitable diene monomers include 1,3-butadiene, chloroprene, isoprene,2,3-dimethyl-1,3 butadiene, piperylene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like and mixtures thereof. Especiallypreferred is 1,3-butadiene due to its availability, effectiveness andfavorable cost. The flexible block or blocks can generally have amolecular weight of from about 15,000 to about 120,000, and moredesirably a molecular weight of from about 50,000 to about 100,000.Molecular weights above 120,000 may be too viscous to be of practicalutility.

The block copolymers used to form some low profile additives of theinvention, in addition to having at least one flexible block, generallyhave at least one "A" monovinyl aromatic block. The monovinyl aromaticblock or blocks generally have a molecular weight of from about 10,000to about 50,000, and more preferably from about 15,000 to about 40,000,with lower molecular weights being preferred, i.e. 10,000 to about30,000, and more preferably from about 15,000 to about 25,000 for eachflexible block of a di-, tri- or multiblock copolymer. The monovinylaromatic A blocks are generally polymerized from monomers containingfrom about 8 to about 12 carbon atoms. Examples of suitable monomersinclude styrene, α-methylstyrene, 3-methylstyrene, 4-n-propylstyrene,and the like, with styrene being preferred because of its availabilityand effectiveness.

The block copolymers used to form some low profile additives of theinvention can be prepared according to various methods well known in theart such as are disclosed in U.S. Pat. Nos. 2,975,160; 3,265,765; and3,280,084. Polymerization of the block copolymers can be hydrocarbylalkali metal initiated, or free radical initiated. The polymerization ofthe block copolymers can be by solution, suspension or emulsionprocesses, and can be conducted as a batch process, as a continuousprocess, or a combination thereof. Additionally, various commerciallyavailable block copolymers having a monovinyl aromatic block and aconjugated diene block can be utilized. Examples of commerciallyavailable block copolymers suitable for use with the invention include,for example, an approximately 50 percent styrene-butadiene diblock/50percent styrene-butadiene-styrene triblock mixture available from theShell Chemical Company and sold under the trademark "Kraton D1300X"; astyrene-butadiene diblock/triblock copolymer mixture also available fromShell Chemical Company and sold under the trademark "Kraton DX1118" anda styrene-butadiene multiblock star copolymer available from theFirestone Synthetic Rubber Company and sold under the trademark "Stereon840A."

The disclosed elastomers used to form the low profile additives of theinvention are generally modified to improve compatibility between thelow profile additive and the crosslinked polyester matrix into which itis added. The preferred method of modifying the elastomers to obtain aneffective low profile additive in accordance with the invention is toepoxidize a sufficient quantity of the olefinic double bonds in theflexible block or blocks to substantially prevent or drastically reduceshrinkage during curing of the thermoset composition to provide a curedmolded article having smooth, highly reflective surfaces. The degree ofepoxidation is generally from about 0.5 percent to about 30 percent,desirably from about 1 percent to about 15 percent, and preferably fromabout 2 percent to about 10 percent of the total number of unsaturatedgroups in the flexible B block.

Epoxidation of the diene is generally effected by various known methodssuch as reaction with an oxidizing agent such as a peracid such asm-chloroperbenzoic acid, peracetic acid, or with hydrogen peroxide inthe presence of a carboxylic acid such as acetic acid or formic acidwith or without a catalyst such as sulfonic acid, p-toluene sulfonicacid, phosphoric acid and the like. Carboxylic anhydrides can beemployed as an alternative to the corresponding carboxylic acids toprovide a higher concentration of peracids formed in situ than for thecorresponding carboxylic acids. The preferred oxidizing agent forepoxidizing the elastomers to form the low profile additives of theinvention is meta-chloroperbenzoic acid.

A solvent for both the oxidizing agent and the elastomeric blockcopolymer to be epoxidized is required. Suitable solvents forepoxidizing the block copolymer generally include aromatic solvents suchas chlorobenzene and the like. The presently preferred solvent for usewith the meta-chloroperbenzoic acid is 1,2-dichloroethane.

Known methods for epoxidizing a diene polymer or diene blocks of a blockcopolymer which can be used in practicing the invention are generallydisclosed, for example, in U.S. Pat. Nos. 4,051,199; 4,131,725;4,341,672 and 4,833,210, and in the following articles: 1) "CatalyticEpoxidation of Styrene-Butadiene Triblock Copolymer with HydrogenPeroxide", Xigao Jian and Allan S. Hay, Dept. of Chemistry, McGillUniversity, Montreal, Quebec, "Journal of Polymer Science: Part A:Polymer Chemistry", Vol. 29, pp. 1183-1189 (1991) John Wiley & Sons,Inc.; 2) "Epoxidation of Polybutadiene and Styrene-Butadiene TriblockCopolymers with Monoperoxyphthalic Acid: Kinetic and Conformation Study"Wen-Kuei Huang, Ging-Ho Hsiue, and Wei-Hsin Hou, Dept. of ChemicalEngineering, National Tsing Hua University, Hsinchu 30043, Taiwan,Republic of China, "Journal of Polymer Science: Part A: PolymerChemistry", Vol. 26, pp. 1867-1883 (1988) John Wiley & Sons, Inc.; and3) "Epoxidation of Bromostyrene--Butadiene Coteloimers", H. N. Nae, M.Goldman, and D. Vofsi, Dept. of Materials Research, The WeizmannInstitute of Science, Rehovot, Israel, "Journal of Polymer Science: PartA: Polymer Chemistry" Vol. 24 pp. 1239-1249 (1986) John Wiley & Sons,Inc.

The preferred method of epoxidizing the elastomers to form the lowprofile additives of the invention involves separately dissolving theoxidant and elastomer in suitable solvents at room temperature, thenadding the oxidant to the elastomer at a subambient temperature such asabout -20° C., thoroughly mixing the dissolved oxidant and elastomer,then heating in an inert atmosphere to an elevated temperature,preferably between about 35° C. and about 50° C. to react the oxidizingagent with the unsaturated backbone and epoxidized same. The by-productis an acid which can be removed by various known means such as solventextraction. The epoxidized elastomer can also be isolated by methodssuch as coagulation and steam stripping.

The amount of low profile additive used to eliminate shrinkage and toproduce a cured article having very smooth, Class A surfaces, andgenerally ranges from about 3 to 20 percent by weight, desirably from 5to 15 percent by weight, and preferably from 7 to about 12 percent byweight based upon the total weight of the thermosetting compositionwithout fillers or fibers, i.e. based upon the total weight of theunsaturated polyester, the styrene or other crosslinking agent, and thelow profile additive. This level provides another important advantage ofthe invention since it is approximately one-half of the amount ofpolyvinyl acetate low profile additives required by the prior art.

In accordance with another aspect of the invention, the oxirane groupsof the epoxidized elastomers can be further reacted with low molecularweight monocarboxyl or monohydroxyl terminated unsaturated polyesteroligomers to form a graft copolymer with the unsaturated polyesterchains being grafted to the flexible epoxidized elastomer. Themonofunctional terminated unsaturated polyesters which can be used toform the graft copolymer are generally well known in the art and aregenerally similar to the hereinafter described unsaturated polyestersused as the matrix material for the thermoset compositions. An exampleof a suitable monocarboxyl terminated unsaturated polyester which can beutilized is a poly(propylene maleate/fumarate) which is about 99.1percent furmarate polyester which is sold by GenCorp under thedesignation B550-125A-12. The resulting graft copolymer has been foundto achieve a balance between shrinkage and surface characteristics, andmechanical properties, which provides a combination of properties whichmight be desirable for certain applications.

In order to achieve adequate shrinkage and good surface characteristicsof the cured invention, it has been found that compatibilizing agentsmust also be added to the thermosetting composition. It is believed thatthe compatibilizing agents improve the solubility of the low profileadditive in the uncured thermosetting composition which contains mostlyunsaturated polyester and a suitable vinyl addition crosslinking agentsuch as styrene monomer. This increased solubility with the uncuredthermosetting composition is, in turn, believed to promote uniformdistribution of the low profile additive throughout the uncuredthermosetting composition and to inhibit agglomeration of the lowprofile additive, thus ensuring uniform properties, and small particlesize for the low profile additive. The compatibilizing agent may alsopromote adhesion between the low profile additive which exists as adispersed particulate phase and the surrounding matrix, to ensure thatcavitation during shrinkage of the curing polyester occurs predominatelywithin the elastomeric low profile additive rather than at the interfacebetween the low profile additive and the cured polyester matrix.

The compatibilizing agent which functions to retard shrinkage isgenerally a copolymer having a first constituent which is compatible orreactive with the unsaturated polyester of the uncured thermosettingcomposition, and a second constituent which is compatible with theelastomer of the low profile additive. The compatibility of thecompatibilizer with both the low profile additive and the unsaturatedpolyester helps to promote uniform distribution of the low profileadditive and to minimize the particle sizes of the low profile additive.The compatibilizing agent is preferably a graft copolymer wherein thepolyester compatible constituents are grafted or adducted to a flexiblepolymer backbone. The backbone is generally formed from monomeric unitssimilar to or more preferably identical with those used to form theelastomer of the low profile additives and the same is herebyincorporated. Polybutadiene is the preferred backbone for the graftcopolymer compatibilizer, however, the backbone polymer of thecompatibilizing agent can generally be any type of rubber such as onemade from one or more conjugated dienes having 4 to 10 carbon atoms,nitrile rubber forming monomers, hydrogenated diene rubbers, and thelike. The molecular weight of the flexible polymer backbone is generallyfrom about 1,000 to 10,000 and preferably from about 4,000 to 8,000. Thepolyester compatible constituents which are grafted to the flexiblepolymer backbone are preferably formed by adding on to the flexiblebackbone, and polymerizing or oligomerizing anhydride monomers having 4to 10 carbon atoms, with maleic anhydride being preferred. An example ismaleic anhydride modified polybutadiene Ricon 131MA17 manufactured byColorado Chemicals Co. The addition of the anhydride is via an additionmechanism using suitable free radical initiators known to the art and tothe literature.

Alternatively, the compatibilizing agent can be a di- or triblockcopolymer having a flexible polymer block which is compatible with theelastomer of the low profile additive, and a polyester or polyanhydrideblock which is compatible with the unsaturated polyester before curing.

The amount of compatibilizer utilized depends on the amount of lowprofile additive used and is generally that amount sufficient to promotegood dispersion of the low profile agent within, and good adhesion ofthe low profile agent with, the polyester matrix. Generally, the amountof compatibilizer used is from about 5 to about 25 percent, andpreferably from about 10 to about 15 percent by weight, based on thetotal weight of the low profile additive and the compatibilizing agent.

The unsaturated polyester resins in which the low-profile additives ofthe invention can be utilized are well known in the art and includethose derived by condensation of unsaturated dibasic acids or anhydridescontaining 4 to 9 carbon atoms with polyols including dihydroxy andtrihydroxy compounds containing 2 to 12 carbon atoms. The polyester mayinclude in the polymeric chain varying proportions of other saturated oraromatic dibasic acids and anhydrides which are not subject tocrosslinking. Examples of unsaturated dibasic acids include maleic,chloromaleic and fumaric acid with maleic anhydride, maleic acid, andfumaric acid being preferred. Aromatic and saturated acids andanhydrides which are exemplary of noncrosslinking moieties within theunsaturated polyester copolymer include phthalic anhydride, orthiophthalic acid, isophthalic acid, terephthalic acid,endomethylene-tetrahydrophthalic anhydride, tetrachlorophthalicanhydride, adipic acid, succinic acid, and the like. Any of a variety ofwell known polyols including di- and tri-hydroxy compounds containing 2to 9 carbon atoms can be used for condensation with the diacids toproduce unsaturated polyesters which can be used advantageously with theinvention. Examples include ethylene glycol, propylene glycol, 1,2, 1,3and 1,4-butadienols, neo-pentyl glycol, diethylene ether diol,trimethylol propane, and the like with propylene glycol being preferred.Various well known method may be employed to produce unsaturatedpolyesters which are suitable for use with the invention.

The crosslinkable polyester resin systems in which the elastomericlow-profile additives of the invention can be utilized generallycomprise a solution formed by dissolving the unsaturated polyester in asolvent comprising at least one polymerizable monomer which iscopolymerizable with the dissolved polyester, i.e. the polymerizablemonomer acts both as a solvent and a reactant which copolymerizes withthe unsaturated groups along the polyester chain. Polymerizable monomerswhich can be utilized as a combination solvent and crosslinker agent forunsaturated polyesters include ethylenically unsaturated compoundscontaining from 3 to 12 carbon atoms. Examples of suitable crosslinkermonomers include styrene, α-methylstyrene, methylmethacrylate, vinylacetate, allyl esters of phthalic, adipic, maleic, malonic and cyanuricacids, with styrene being preferred. Commercially available unsaturatedpolyester resins which are normally sold as a liquid solution can beused with the low-profile additives of the invention.

The cured article formed by using the low profile additives andcompatibilizing agents, in a generally otherwise conventionalunsaturated polyester thermosetting composition, in accordance with theinvention, provides a cured article having unique characteristics andmorphology, wherein the low profile additive exists as small discreteparticles distributed throughout the matrix, and with shrinkagecompensation occurring substantially through cavitation or voidformation within the individual particles of the low profile additive.Further, it has been found that the low profile additive particles,dispersed throughout cured articles formed from thermosettingcompositions in accordance with the invention, generally have highprobability of containing voids. That is, generally at least 50 percent,desirably at least 70 percent, and preferably at least 80 percent or 90percent of the particles have at least one-void therein. Because thevoids are hidden within the tough elastomeric low profile additive,mechanical properties such as impact strength are not reduced to asignificant extent. In particular, the cured articles made in accordancewith the principles of the invention generally have a fracture toughnesswhich is at least 70 percent, desirably at least 75 or 80 percent, andpreferably at least 90 percent, and in certain instances at least about100 percent, of the fracture toughness of a cured article formed from athermosetting composition which does not have any low profile additivebut which is otherwise identical with the invention. The fracturetoughness, that is K_(1c), of the cured compositions of the presentinvention is generally at least 0.35; desirably at least 0.40; andpreferably at least 0.45 M-Pa-m^(1/2).

The particle size of the low profile additive is important to thesurface characteristics of the cured polyester article and once it hasbeen dispersed with the compatibilizing agent in the unsaturatedpolyester and cured, it generally is less than 20 microns, preferablyfrom about 0.5 to about 10 microns, and more preferably is from about0.5 to about 5 microns in size. These lower particle sizes generallyprovide smoother surfaces which are desired for automotive body panels,for example.

The thermosetting molding compositions of the present inventioncontaining the curable unsaturated polyester, the ethylenicallyunsaturated crosslinking agent, the low profile additive of the presentinvention and the compatibilizin agent once mixed have good phasestability, that is they are shelf stable for extended periods of time asup to about 8, 10 and even 12 or 15 hours. In other words, the lowprofile additive exists as small discrete particles for such periods oftime.

Fibers can be added to the composition for added strength and stiffness.Examples of fibers which can be utilized in this invention generallyinclude any reinforcing fiber such as glass, aramid, nylon, polyester,graphite, boron, and the like. Fiber structure suitable forincorporation into the matrix include generally individual fibers,various types of woven fibers, or any general type of nonwoven fibers.Included within the woven class is any general type of woven fabrics,woven roving, and the like. Generally included within the nonwoven classare chopped strands, random or wound continuous filaments or rovings,reinforcing mats, nonreinforcing random mats, fiber bundles, yarns,nonwoven fabrics, etc. Coated fiber bundles, comprising about 5 to about50 or 150 strands, each having about 10 to about 50 fibers, bondedtogether with conventional sizing agents such as various amino silanes,are preferred. Chopped glass fibers are preferred with a desirablelength of 0.5" to 2.0" and preferably 1". The fibers may comprise fromabout 5 percent up to about 60 percent by weight of the composite andpreferably from 20 percent to 50 percent by weight of the composite. Thespecific quantity of fiber structure in the composite can be variedconsistent with the physical properties desired in the final compositemolded article.

Other additives which can also be utilized in effective amounts areknown to the art and to the literature and include internal mold releaseagents such as zinc stearate; viscosity reducers or viscosity modifiers;free radical inhibitors; mineral fillers such as calcium carbonate,Dolomite, clays, talcs, zinc borate, perlite, vermiculite, hollow glassspheres, solid glass microspheres, hydrated alumina, carbon black, andthe like. Often calcium carbonate is used in substantial amounts.Viscosity modifiers can be compounds such as MgO dispersions thatthicken the unsaturated polyester resins during aging. The typicalviscosity reducers used in this specification are long chain aliphaticmonocarboxylic acids or saturated polyesters with acid groups. Thefillers can be present from 0 to about 80 weight percent, and desirablyfrom 20-70 weight percent of the total composition weight. Free radicalinhibitors are included to modify cure cycles by providing cure delayand moderating the cure exotherm. These free radical inhibitors can bepresent from 0.001 to 0.2 parts per 100 parts by weight of unsaturatedpolyester resins or vinyl ester resins and ethylenically unsaturatedmonomers in the composition. The free radical inhibitors includebenzoquinone, hydroquinone, and similar substituted quinones.

Conventional catalysts can be used to cure the composition containingthe unsaturated polyester. Examples of such catalysts include organicperoxides and hydroperoxides such as benzoyl peroxide, dicumyl peroxide,cumene hydroperoxide, tert-butylperbenzoate, paramenthane hydroperoxide,and the like, used alone or with redox systems; diazo compounds such asazobisisobutyronitrile, and the like; persulfate salts such as sodium,potassium, and ammonium persulfate, used alone or with redox systems;and the use of ultraviolet light with photo-sensitive agents such asbenzophenone, triphenylphosphine, organic diazos, and the like. Whencuring is done in a mold at elevated temperatures, then the temperaturecan desirably vary from about 30° C. to about 160° C. and is preferablyfrom about 80° C. to about 150° C. Alternatively, when photo sensitiveagents are used, lower temperatures can be used. The amount of catalystused can vary from about 0.1 to about 5 parts and is desirably 0.5 toabout 2.0 parts by weight per 100 parts of resins and polymer formingcomponents in the composition.

The general procedure for mixing the composition of the presentinvention involves dissolving the unsaturated polyester, and any otherpolymeric components in the ethylenically unsaturated monomer. Thecomposition is then well mixed. The catalyst for the free radicalcrosslinking reaction can be added to the mix at any of the variousstages so long as the temperature of the mix is not so high as to startfree radical crosslinking. Fillers can also be added at this stage.

Compositions made in accordance With the invention can be utilized inresin transfer molding, bulk molding, sheet molding, thick molding, andthe like. The composite material of the invention provides a toughenedmolding material having better crack resistance, fracture toughness,strength and modulus and can be molded as automotive components, e.g.body panels and automotive structural components (such as load bearingsupport members), aircraft components, housings for various electricaland household goods, and sporting goods.

The invention will be more fully understood from the followingillustrative examples, wherein various low profile additives or lowprofile additive systems are compared to each other and to a similarcomposition which is free of low profile additives. In each example,cured articles were formed from a curable polyester compositionconsisting of an unsaturated polyester, styrene crosslinker, curingagents, and a low profile additive or low profile additive system. Theunsaturated polyester used in each example was Aristech MR13006available from Aristech Chemical. Aristech MR13006 is an unsaturatedpolyester supplied as a 60 percent by weight solution in styrene, and iscomprised of 30 percent by weight propylene glycol, 7 percent by weightethylene glycol, 4 percent by weight dipropylene glycol, 6 percent byweight maleic acid, and 53 percent by weight fumaric acid. In eachexample, the Aristech MR13006 was mixed with an amount styrene needed toraise the molar ratio of styrene to unsaturation in the unsaturatedpolyester to about 3.5. The curing agents for each example comprised 1.0phr of tert-butyl perbenzoate, 0.5 to 1.0 phr of methyl ethyl ketoneperoxide as a 50 percent by weight solution in dimethyl phthalate, and0.05 to 0.10 phr of cobalt naphthenate as a 6 percent by weight solutionin mineral spirits and hexylene glycol. To simplify the comparisonbetween the various low profile additives, fillers, fibers, mold releaseagents and maturation agents, all of which are normally present inpolyester molding compounds, were not used in any of the examples.

For each of the following examples the unsaturated polyester, styreneand curing agents were mixed in the amounts set forth above along withone of the various low profile additives or low profile additivesystems, degassed and then cast in vertical molds which were air ovencured for 2 hours at 85° C., then 1 hour at 120° C. and finally for 1hour at 140° C.

EXAMPLE 1

Because the object of the present invention is to find a low profileadditive which achieves low or no shrinkage, provides a cured articlehaving a class A surface finish, and retains the inherent mechanicalproperties of polyester, a control, comprising castings formed from amolding composition as set forth above but free of any low profileadditives was prepared.

EXAMPLE 2

A second control, representative of the most commonly used low profileadditives, was prepared by adding a poly(vinyl acetate) available fromUnion Carbide and sold under the trademark "Neulon T+" to the curablepolyester composition set forth above. The amount of "Neulon T+" usedwas 35 percent by weight based on the combined weight of the unsaturatedpolyester, the styrene and the poly(vinyl acetate). Thus, the amount ofthe poly(vinyl acetate) which was added was 14 percent by weight.

EXAMPLES 3-4

Examples 3 and 4 establish that unmodified styrene-butadiene blockcopolymers, which are commonly used to enhance toughness, do not provideadequate low profile effect by themselves. For Example 3, "KRATOND1300X" was added to the curable polyester composition as previously setforth. The amount of "KRATON D1300X" used was 7 percent by weight basedon the combined weight of the unsaturated polyester, the styrene, andthe "KRATON D1300X". For Example 4, "Stereon 840A" was used in thecurable polyester composition in an amount so that the "Stereon 840A"represented 7 percent of the combined weight of the unsaturatedpolyester, the styrene, and the "Stereon 840A".

EXAMPLES 5-8

Examples 5-8 establish that epoxidized styrene-butadiene blockcopolymers by themselves do not provide adequate low profile effect.Examples 5-8 were prepared in a manner similar to Examples 3 and 4,using the same amounts of unsaturated polyester, styrene, andstyrene-butadiene block copolymers, except that the styrene-butadieneblock copolymers were epoxidized. For Example 5, "Kraton D1300X" was 1percent epoxidized with n-chlorperbenzoic acid. The level of epoxidationis expressed as the mole percent of the butadiene units converted toepoxy groups. For Example 6, "Kraton D1300X" was 10 percent epoxidized,and for Examples 7 and 8, "Stereon 840A" was epoxidized to 0.2 percentand 12.5 percent epoxidation, respectively. In each of Examples 5-8, theamount of epoxidized styrene-butadiene block copolymer used was suchthat the styrene-butadiene block copolymer represented 7 percent of thecombined weight of the unsaturated polyester, the styrene and theepoxidized styrene-butadiene block copolymer.

EXAMPLES 9 AND 10

Examples 9 and 10 establish that unmodified styrene-butadiene blockcopolymers even when used in conjunction with a compatibilizing agent donot provide adequate low profile effect. Example 9 is a curablepolyester composition as set forth above except that unmodified "KratonD1300X" was added such that the "Kraton D1300X" represents 7 percent ofthe combined weight of the polyester, styrene and "Kraton D1300X", and acompatibilizing agent was added such that the compatibilizing agentrepresents 0.93 percent by weight of the combined weight of thepolyester, styrene and "Kraton D1300X". Example 10 is identical toExample 9, except that unmodified "Stereon 840A" was substituted for"Kraton D1300X".

The compatibilizing agent used in Examples 9 and 10 was a low molecularweight polybutadiene adducted with maleic anhydride. The compatibilizingagent is commercially available from Colorado Chemicals and sold underthe trademark "RICON 131MA17". "RICON 131MA17" has a number averagemolecular weight of 6,500, with 20 percent 1,2-butadiene units and 80percent 1,4 cis and 1,4 trans butadiene units. Seventeen percent byweight of the 1,4 units were modified with maleic anhydride, i.e.approximately 11 maleic anhydride groups per molecule.

EXAMPLES 11 AND 12

Examples 11 and 12 represent preferred embodiments of the inventionwherein the low profile additive system of the invention, comprising anepoxidized styrene-butadiene block copolymer and the maleicanhydride-polybutadiene ("RICON 131MA17") compatibilizing agent, areutilized. Examples 11 and 12 are generally identical with Examples 9 and10, respectively, except that in the case of Example 11, the "KRATOND1300X" is 10 percent epoxidized and in the case of Example 12 the"STEREON 840a" is 10 percent epoxidized.

For each of the above Examples, the plane-strain fracture toughness,K_(1C), was determined in accordance with ASTM E399-83. Tensile strength(UTS), Young's Modulus (E) and strain-to-failure (Ef) were determinedfor each of the Examples using the procedures of ASTM D638-87.

Each of the above Examples was evaluated for its low profile effect viacasting. For purposes of this evaluation, low profile effect was treatedas a combination of shrinkage and surface appearance. Shrinkage wasassessed only to the extent of determining whether the moldingcomposition shrunk, expanded, or fit the mold exactly after curing.Compositions which did not shrink during curing met the first criterionfor being judged as having acceptable low profile effect. Thosecompositions which shrunk were judged to have unacceptable low profileeffect. Surface appearance was subjectively judged by evaluating thesharpness of a reflected image of a nearby grid. Only those curedcompositions which did not shrink and which exhibited very smoothsurfaces were rated as having acceptable low profile effect.

The results for the mechanical properties and low profilecharacteristics for each of the Examples were summarized in Table 1.

The results show that polyvinyl acetate, while exhibiting excellentsurface appearance and low profile effect, causes a substantialreduction in fracture toughness (K_(1C)) and other mechanicalproperties. Unmodified styrene-butadiene block copolymers exhibit goodmechanical properties but provide poor low profile effect. Both theepoxidized styrene-butadiene block copolymers (Examples 5-8) and theunmodified styrene-butadiene block copolymers used with the maleicanhydride-butadiene compatibilizing agent (Examples 9 and 10 exhibitedbetter low profile effect while retaining good mechanical properties;however, none of these Examples (5-10) provided the very smooth surfacesrequired for certain applications such as for automotive body panels.

The results show that only Examples 11 and 12, which are in accordancewith the invention, provide excellent low profile effects with verysmooth surfaces while exhibiting significantly better mechanicalproperties than do compositions employing polyvinyl acetate low profileadditives.

Table II is similar to Table I except that it relates to the variouscompositions which were molded. As apparent from Table II, Examples 16and 17 which contain the compatibilizing agent exhibit the goodmechanical properties as well as a smooth surface appearance.

                                      TABLE I                                     __________________________________________________________________________    CASTINGS                                                                      __________________________________________________________________________                                   AMT OF                                         EX LPA.sup.1 AMT OF LPA.sup.2                                                                       COMPATIBILIZER                                                                         COMPATIBILIZER.sup.3                                                                     K.sub.1c.sup.4                                                                   UTS.sup.5                                                                         E.sup.6                      __________________________________________________________________________    1  None      --       --       --         0.538                                                                            37.87                                                                             3.95                         2  Polyvinyl 14%      --       --         0.301                                                                            15.44                                                                             2.32                            Acetate                                                                    3  KRATON D1300X                                                                           7%       --       --         0.596                                                                            12.70                                                                             2.11                         4  STEREON 840A                                                                            7%       --       --         0.652                                                                            13.06                                                                             2.03                         5  1% Epoxidized                                                                           7%       --       --         0.644                                                                            12.04                                                                             2.73                            KRATON D1300X                                                              6  10% Epoxidized                                                                          7%       --       --         0.622                                                                            11.51                                                                             2.77                            KRATON D1300X                                                              7  0.2% Epoxidized                                                                         7%       --       --         0.543                                                                            9.75                                                                              2.51                            STEREON 840A                                                               8  12.5% Epoxidized                                                                        7%       --       --         0.588                                                                            8.80                                                                              2.55                            STEREON 840A                                                               9  KRATON D1300X                                                                           7%       RICON131MA17                                                                           0.93       0.532                                                                            12.10                                                                             2.05                         10 STEREON 840A                                                                            7%       RICON131MA17                                                                           0.93       0.437                                                                            20.59                                                                             2.45                         11 10% Epoxidized                                                                          7%       RICON131MA17                                                                           0.93       0.447                                                                            15.81                                                                             2.55                            KRATON D1300X                                                              12 10% Epoxidized                                                                          7%       RICON131MA17                                                                           0.93       0.408                                                                            22.15                                                                             2.51                            STEREON 840A                                                               __________________________________________________________________________               EX                                                                              LPA.sup.1                                                                              Ef.sup.7                                                                          SHRINKAGE                                                                             APPEARANCE                                                                              LPA EFFECT                        __________________________________________________________________________               1 None     1.08                                                                              Shrinks --       Unaccceptable                                 2 Polyvinyl                                                                              0.707                                                                             Expands Very     Acceptable                                      Acetate              Smooth                                                 3 KRATON D1300X                                                                          0.602                                                                             Fits    Rough    Unacceptable                                                 Exactly                                                        4 STEREON 840A                                                                           0.711                                                                             Fits    Rough    Unacceptable                                                 Exactly                                                        5 1% Epoxidized                                                                          0.482                                                                             Fits    Slightly Unacceptable                                    KRATON D1300X                                                                              Exactly Rough                                                  6 10% Epoxidized                                                                         0.459                                                                             Fits    Slightly Unacceptable                                    KRATON D1300X                                                                              Exactly Rough                                                  7 0.2% Epoxidized                                                                        0.483                                                                             Fits    Smooth   Unacceptable                                    STEREON 840A Exactly                                                        8 12.5% Epoxidized                                                                       0.460                                                                             Expands Smooth   Unacceptable                                    STEREON 840A                                                                9 KRATON D1300X                                                                          0.674                                                                             Fits    Smooth   Unacceptable                                                 Exactly                                                        10                                                                              STEREON 840A                                                                           0.930                                                                             Fits    Smooth   Unacceptable                                                 Exactly                                                        11                                                                              10% Epoxidized                                                                         0.749                                                                             Fits    Very     Acceptable                                      KRATON D1300X                                                                              Exactly Smooth                                                 12                                                                              10% Epoxidized                                                                         1.074                                                                             Fits    Very     Acceptable                                      STEREON 840A Exactly Smooth                                      __________________________________________________________________________     .sup.1 Low profile additive used                                              .sup.2 Based on the combined weight of the unsaturated polyester, styrene     and LPA                                                                       .sup.3 Based on the combined weight of the unsaturated polyester, styrene     and LPA                                                                       .sup.4 In units of MPam.sup.                                                  .sup.5 In units of MPa                                                        .sup.6 In units of GPa                                                        .sup.7 Strain to failure in percent elongation                           

                                      TABLE II                                    __________________________________________________________________________    MOLDED SMC                                                                    __________________________________________________________________________                  AMT              AMT OF                                         EX  LPA.sup.1 OF LPA.sup.2                                                                        COMPATIBILIZER                                                                           COMPATIBILIZER.sup.3                                                                     K.sub.1c.sup.4                                                                   UTS.sup.5                        __________________________________________________________________________    13  PVAC      14%   --         --         NA 144 ± 31                      14  KRATON D1300X                                                                           7%    --         --         NA 138 ± 30                      15  STEREON 840A                                                                            7%    --         --         NA 149 ± 27                      16  5% Epoxidized                                                                           7%    RICON      0.93       NA 163 ± 75                          KRATON D1300X                                                             17  5% Epoxidized                                                                           7%    RICON      0.93       NA 174 ± 39                          STEREON 840A                                                              __________________________________________________________________________                                         Surface                                                                 Expansion                                                                           Undulations                                                                          Surface                           EX       LPA.sup.1 E.sup.6                                                                             Ef.sup.7                                                                            (Mils/in)                                                                           (Microns)                                                                            Smoothness                        __________________________________________________________________________    13       PVAC      7.10 ± 1.03                                                                      2.39 ± 0.40                                                                      1.2   ˜0.1                                                                       to 0.2                                                                            Good                              14       KRATON D1300X                                                                           6.90 ± 0.83                                                                      2.32 ± 0.36                                                                      0.4   ˜1                                                                         to 5                                                                              Poor                              15       STEREON 840A                                                                            7.24 ± 0.90                                                                      2.30 ± 0.22                                                                      0.3   ˜1                                                                         to 5                                                                              Poor                              16       5% Epoxidized                                                                           7.38 ± 1.17                                                                      2.40 ± 0.20                                                                      0.5   ˜0.1                                                                       to 0.2                                                                            Good                                       KRATON D1300X                                                        17       5% Epoxidized                                                                           7.86 ± 1.66                                                                      2.54 ± 0.33                                                                      0.3   ˜0.1                                                                       to 0.2                                                                            Good                                       STEREON 840A                                                         __________________________________________________________________________

While in accordance with the Patent Statutes, the best mode andpreferred embodiment has been set forth, the scope of the invention isnot limited thereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A thermosetting molding composition, comprising:acurable unsaturated polyester; an ethylenically unsaturated crosslinkingagent; about 3 to 20 weight percent of a low profile additive based uponthe weight of the unsaturated polyester, ethylenically unsaturatedcrosslinking agent, and low profile additive which low profile additiveis either one or more epoxidized elastomers having a number averagemolecular weight from 15,000 to 200,000 polymerized from at least oneconjugated diene monomer and optionally from addition polymerizablemonomers or one or more epoxidized block thermoplastic elastomers havingat least one flexible block having a number average molecular weightfrom 15,000 to 120,000 polymerized from one or more conjugated dienemonomers having from 4 to about 12 carbon atoms and having at least onemonovinyl aromatic block polymerized from at least one monovinylaromatic monomer having from 8 to about 12 carbon atoms; and about 5 to25 weight percent of a compatibilizing agent based upon the weight ofthe low profile additive and compatibilizing agent which compatibilizingagent is a copolymer having at least a first constituent of grafted,adducted, or polymerized anhydrides moiety having 4 to 10 carbon atomsper anhydride or of polyester which first constituent is compatible orreactive with the unsaturated polyester of the thermosetting moldingcomposition, and at least a second constituent which is a polymer ofnumber average molecular weight from 1,000 to 10,000 from at least oneconjugated diene and optionally from addition polymerizable monomers andbeing compatible with the elastomer or the flexible block of the lowprofile additive.
 2. The composition of claim 1, wherein the low profileadditive is said one or more epoxidized thermoplastic elastomers andeach flexible block thereof has a number average molecular weight offrom about 15,000 to 120,000 before epoxidation and each monovinylaromatic block has a number average molecular weight of from about10,000 to about 50,000, and wherein the degree of epoxidation is fromabout 0.5 percent to about 30 percent of the total number of unsaturatedgroups in the flexible blocks of the block copolymer.
 3. The compositionof claim 2, wherein the low profile additive is one or more epoxidizedthermoplastic elastomers of styrene and butadiene, wherein the amount ofepoxidation is from about 1 to about 15 percent, wherein unsaturatedpolyester is made from propylene glycol and maleic anhydride, maleicacid, or fumaric acid or combinations thereof, wherein the ethylenicallyunsaturated crosslinking agent is styrene, and wherein the amount ofsaid low profile is from about 5 percent to about 15 percent by weight.4. The composition of claim 3, wherein the compatibilizing agent is acopolymer having a diene polymer backbone made from conjugated dieneshaving from 4 to 10 carbon atoms, wherein the constituent which iscompatible or reactive with the unsaturated polyester being grafted oradducted onto the unsaturated groups of the diene polymer backbone ismaleic anhydride, or an oligomer thereof, or a low molecular weightpolymer thereof, or combinations thereof, wherein the number averagemolecular weight of the diene polymer backbone is from about 4,000 toabout 8,000, and wherein the amount of compatibilizer in the compositionis from about 5 percent to about 25 percent by weight based on thecombined weight of the low profile additive and the compatibilizingagent.
 5. The composition of claim 4, which is phase stable up to about10 hours.
 6. An automotive component, comprising; the cured compositionof claim
 4. 7. The composition of claim 2, wherein the compatibilizingagent is a copolymer having a diene polymer backbone made fromconjugated dienes having from 4 to 10 carbon atoms, and wherein theconstituent which is compatible or reactive with the unsaturatedpolyester being grafted or adducted onto the unsaturated groups of thediene polymer backbone is an anhydride having from 4 to 10 carbon atoms,or an oligomer thereof, or low molecular weight polymer thereof, orcombinations thereof.
 8. The composition of claim 1, wherein thecomposition is phase stable up to about 12 hours.
 9. The composition ofclaim 1, wherein the compatibilizing agent is a copolymer having a dienepolymer backbone with the constituent which is compatible with theunsaturated polyester being grafted or adducted to the diene polymerbackbone.
 10. An automotive component, comprising; the cured compositionof claim
 1. 11. A molded thermoset article having improved mechanicalproperties and a smooth surface finish, the molded thermoset articlecomprising; a crosslinked polyester matrix; from 3 to 20 weight percentof low profile additive particles dispersed throughout the crosslinkedpolyester matrix based upon the weight of the crosslinked polyestermatrix and the low profile additive, said low profile additive particlespolymerized from at least one conjugated diene monomer having from 4 to10 carbon atoms and optionally from addition polymerizable monomerswhich low profile additive is one or more epoxidized elastomers ofnumber average molecular weight of from 15,000 to 200,000 or is one ormore epoxidized thermoplastic elastomer block copolymers having at leastone flexible block of number average molecular weight of 15,000 to120,000, at least 50 percent of said particles which have a voidtherein; and a grafted compatibilizing agent comprising (a) a polymer orcopolymer of number average molecular weight of from 1,000 to 10,000made from at least one diene monomer having from 4 to 10 carbon atomsand optionally from addition polymerizable monomers, and (b) a componentof grafted or adducted anhydrides, oligomer thereof, or low molecularweight polyester thereof having from 4 to 10 carbon atoms per anhydride.12. The molded article of claim 11, wherein the low profile additive issaid one or more thermoplastic elastomer block copolymers and has atleast one flexible block polymerized from one or more conjugated dienemonomers having from 4 to about 12 carbon atoms and at least onemonovinyl aromatic block polymerized from at least one monovinylaromatic monomer having from 8 to about 12 carbon atoms, and wherein thelow profile additive has an average particle size of less than about 20microns.
 13. The molded article of claim 12, wherein each flexible blockof the epoxidized thermoplastic block copolymers has a number averagemolecular weight of from about 15,000 to 120,000 before epoxidation andeach monovinyl aromatic block has a number average molecular weight offrom about 10,000 to about 50,000; wherein the degree of epoxidation isfrom about 0.5 percent to about 30 percent of the total number ofunsaturated groups in the flexible blocks; and wherein the amount of lowprofile additive is from about 3 percent to about 20 percent based uponthe weight of the crosslinked polyester matrix and the low profileadditive.
 14. The molded article of claim 13, wherein thecompatibilizing agent is a copolymer having a diene polymer backbone anda constituent which is grafted or adducted onto the diene polymerbackbone; wherein the grafted or adducted constituent is a maleicanhydride molecule having from 4 to about 10 carbon atoms, or anoligomer thereof, or a low molecular weight polymer segment thereof, orcombinations thereof; wherein the number average molecular weight of theflexible polymer backbone is from about 4,000 to about 8,000, whereinthe amount of compatibilizing agent in the article is from about 5percent to about 25 percent by weight based on the combined weight ofthe low profile additive and the compatibilizing agent, wherein the lowprofile additive is an epoxidized block copolymer styrene and butadiene,wherein the amount of epoxidation is from about 1 to about 15 percent,wherein unsaturated polyester is made from propylene glycol and maleicanhydride, maleic acid, or fumaric acid or combinations thereof, whereinthe ethylenically unsaturated crosslinking agent is styrene, wherein theamount of said low profile is from about 5 percent to about 15 percentby weight, wherein at least 80 percent of the low profile particles havea void therein.
 15. An automobile component comprising; the moldedthermoset article of claim
 14. 16. An automobile component comprising;the molded thermoset article of claim
 13. 17. The molded article ofclaim 12, wherein the compatibilizing agent is a copolymer having adiene diene polymer backbone and a constituent which is grafted oradducted onto the diene polymer backbone; wherein the grafted oradducted constituent is an anhydride molecule having from 4 to about 10carbon atoms, or an oligomer thereof, or a low molecular weight polymersegment thereof, or combinations thereof; and wherein the number averagemolecular weight of the diene polymer backbone is from about 4,000 toabout 8,000.
 18. An automobile component comprising; the moldedthermoset article of claim
 11. 19. A method of forming a molded articlehaving good mechanical properties and a smooth surface finish,comprising the steps of;blending a curable unsaturated polyester; anethylenically unsaturated crosslinking agent; about 3 to 25 weightpercent of a low profile additive based upon the weight of theunsaturated polyester, crosslinking agent, and low profile additive,said low profile additive being either one or more epoxidized elastomershaving a number average molecular weight of from 15,000 to 200,000 andmade from at least one conjugated diene having from 4 to 12 carbon atomsand optionally from addition polymerizable monomers or one or moreepoxidized thermoplastic elastomer block copolymers having at least oneflexible block having a number average molecular weight from 15,000 to120,000 polymerized from at least one or more conjugated diene monomershaving from 4 to about 12 carbon atoms and having at least one monovinylaromatic block polymerized from at least one monovinyl aromatic monomerhaving from 8 to about 12 carbon atoms; and a compatibilizing agent inamounts from about 5 to about 25 weight percent of based on the weightof the low profile additive and the compatibilizer which is a copolymerhaving at least a first constituent of grafted or adducted anhydridehaving from 4 to 10 carbon atoms per anhydride unit or a polyesterthereof which is compatible or reactive with the unsaturated polyesterof the thermosetting molding composition; and at least a secondconstituent which is a polymer of number average molecular weight from1,000 to 10,000 derived from at least one conjugated diene monomer andoptionally from one or more addition polymerizable monomers and beingcompatible with the elastomer or the flexible block of the low profileadditive; and heating the blend to a sufficient temperature and for anamount of time sufficient to form a crosslinked polyester matrix. 20.The method of claim 19, wherein the low profile additive is saidthermoplastic elastomer and each flexible block of the epoxidized blockcopolymer has a number average molecular weight of from about 15,000 to120,000 before epoxidation, and each monovinyl aromatic block has anumber average molecular weight of from about 10,000 to about 50,000;wherein the degree of epoxidation is from about 0.5 percent to about 30percent of the total number of unsaturated groups in the flexible blocksof the epoxidized block copolymer; wherein the low profile additiveexists as particles, at least 50 percent of which have voids, dispersedwithin the article having an average particle size of less than about 20microns; and wherein the amount of the low profile additive is fromabout 3 percent to about 20 percent based upon the weight of theunsaturated polyester, the crosslinking agent and the low profileadditive.
 21. The method of claim 20, wherein the compatibilizing agentis a copolymer having a diene polymer backbone made from conjugateddienes having from 4 to 10 carbon atoms with the constituent which iscompatible or reactive with the unsaturated polyester being grafted oradducted onto the diene polymer backbone; wherein the grafted oradducted constituent is an anhydride molecule having from 4 to about 10carbon atoms, or an oligomer thereof or a low molecular weight polymersegment thereof, or combinations thereof; and wherein the number averagemolecular weight of the flexible polymer backbone is from about 1,000 toabout 10,000.
 22. The method of claim 21, wherein the amount ofcompatibilizer in the composition is from about 5 percent to about 25percent by weight based on the combined weight of the low profileadditive and the compatibilizing agent, wherein the low profile additiveis an epoxidized block copolymer styrene and butadiene, wherein theamount of epoxidation of the low profile additive is from about 1 toabout 15 percent, wherein the anhydride molecule is maleic anhydride,wherein unsaturated polyester is made from propylene glycol and maleicanhydride, maleic acid, or fumaric acid or combinations thereof, whereinthe ethylenically unsaturated crosslinking agent is styrene, and whereinthe amount of said low profile is from about 5 percent to about 15percent by weight.